1. Field of the Invention
The present invention relates to a wireless positioning method and apparatus using wireless sensor network, and more particularly, to a wireless positioning method and apparatus using a wireless sensor network, wherein a localization error generated in a general wireless centroid localization (WCL) algorithm is prevented.
2. Description of the Related Art
Generally, since the sensor in wireless sensor network has low power, low complexity, and intelligent characteristics, almost all the positioning algorithms using the wireless sensor network will require a simple structure and a quick operation speed. Location information of an anchor node whose actual position is known is usually used to estimate a position of an unknown node in a sensor network. Basically, anchor nodes determine their actual positions by using global positioning system (GPS) information or pre-stored position information. In reality, installation of anchor nodes in most positioning is inevitable.
A representative algorithm that satisfies the above requirements from among wireless positioning algorithms for a wireless sensor network, which has been studied so far, is wireless centroid localization (WCL) algorithm. The WCL algorithm is effective in terms of speed and resources since a positioning operation is simply performed only by using coordinate information of each anchor node, which is different from other algorithms.
A reception range of an unknown node that is a positioning target is a circle based on the unknown node. A radius of the circle is indicated as a maximum reception distance limit point (dm). For positioning of the unknown node, the general WCL algorithm only considers anchor nodes within the circle, and uses position information of the anchor nodes. Also, in the general WCL algorithm, it is assumed that the anchor nodes within the circle have the same weight wj, and thus a weight which equals 1 is assigned to the anchor nodes within the circle and a weight which equals 0 is assigned to anchor nodes outside the circle. When N anchor nodes satisfy the above conditions, the general WCL algorithm will be represented by Equation 1 below.
                              P          ⁡                      (                          x              ,              y                        )                          =                                            ∑                              j                =                1                            N                        ⁢                                                  ⁢                                          w                j                            ⁢                                                A                  j                                ⁡                                  (                                      x                    ,                    y                                    )                                                                                        ∑                              j                =                1                            N                        ⁢                                                  ⁢                          w              j                                                          [                  Equation          ⁢                                          ⁢          1                ]            
Here, P(x,y) denotes position coordinates of an unknown node, and Aj(x,y) denotes position coordinates of the j-th anchor node.
FIG. 1 is a graph showing the positioning simulation result of an unknown node using the general WCL algorithm in wireless sensor network of a 90×90 m2 square space environment, wherein 100 anchor sensor nodes are arranged at intervals of 1 m, and 300 unknown sensor nodes are arranged. In FIG. 1, horizontal and vertical axes respectively denote horizontal and vertical areas in a 90×90 m2 square space. ● denotes the position of an anchor node, * denotes the actual position of an unknown node, and ∘ denotes the estimated position of each unknown node using general WCL algorithm. From FIG. 1, the localization error is higher when an unknown node is in the corner region or edge area compared with when it is in the center region of the square space. The increased degree of localization error is indicated by a length of a line connecting ∘ and *.
FIG. 2 is a diagram schematically classifying the wireless sensor network of FIG. 1 into center region (gray region), edge region (white region), and corner region (black region). Here, each sizes of the four corner regions are 10×10 m2, size of the center region is 70×70 m2, and edge regions' are 10×70 m2 or 70×10 m2. The simulation result of the general WCL algorithm under in this environment is shown in FIG. 3.
FIG. 3 is a graph showing an average localization error according to the general WCL algorithm in each area of FIG. 2. In FIG. 3, the horizontal axis denotes a radius of a circle applied to an unknown node, and the vertical axis denotes average localization error. Here, the average localization error is higher when the unknown node is in edge and corner regions than when it is in a center region of a network. In detail, the localization error is highest when the unknown node is in the corner region. In other words, according to the general WCL algorithm, localization error increases near an edge and a corner in the wireless sensor network.
A background technology of the present invention is disclosed in KR 10-1163335.